(1) Field of the Disclosure
The present disclosure generally relates to an electrical enclosure. More particularly, the present disclosure relates to an electrical enclosure where all functional compartments defined within the enclosure are accessible only from the front of the enclosure.
(2) Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Medium voltage electrical components, such as circuit breakers, potential transformers, current transformers, control power transformers, etc., operate, as conventionally understood by one of skill in the art, in a range of about 1,000 volts to about 35,000 volts. A conventional front accessible medium switchgear assembly includes at least a pair of sections (i.e., each an individual metal cabinets having a plurality of compartments) separated from one another by a vertical metal barrier. Each section includes a low voltage compartment and at least one compartment for a medium voltage electrical component both disposed immediately behind doors at the front of the section, and a bus bar compartment disposed in a rear portion of the section, behind low voltage and medium voltage electrical components. At least one of the sections includes a cable connection compartment disposed immediately behind a door at the front of the applicable section. The bus bar compartment and cable connection compartment are configured to extend into immediately adjacent sections. As a result, a conventional medium voltage switchgear assembly occupies a large amount of floor space (i.e., at least two sections width), and requires front and rear access for operation and maintenance (i.e., clearance space at the rear in addition to that required by code, law or regulation). As such, maintenance and space considerations are driving factors in the design of new medium voltage switchgear enclosures, components and equipment. There is a need for constructing a medium voltage switchgear enclosure that makes efficient use of the available floor space and minimizes the time required for inspection, repair and maintenance of components accommodated therein (i.e., requires only a single, front-accessible section).
A certain amount of space is required between adjacent structures, such as walls, and the medium voltage switchgear assembly per the national electric code (NEC) and other local codes. However, allocation of available space is a critical factor in industrial applications, data center facilities and marine equipment, where space is limited and at a premium. Often, an entire room is necessary to be allocated for a bank of medium voltage switchgear assemblies. Consequently, such an allocation of a substantial amount of space, for example, an entire room for the medium voltage switchgear assemblies, each including a plurality of sections, is an undesirable and inefficient use of valuable floor space, especially in healthcare and data-center facilities.
One of skill in the art recognizes that a medium voltage switchgear assembly can be damaged due to an arc flash incident, which is an explosion caused by arcing that generates enormous pressure and temperature within a switchgear assembly that results in significant economic loss due to interruption of energy distribution, and damage of the switchgear assembly and the components or equipment accommodated in the switchgear cabinet. Consequently, maintenance personnel inspecting and servicing the switchgear assembly have to wear protective gear that is bulky and expensive. A typical arc resistant switchgear assembly tends to be very large, for example, each section is 36 inches wide and 94 inches deep and often have heavy sheet metal enclosures, including a continuous vertical metal barrier between adjacent sections of the switchgear assembly. Such switchgear assemblies have multiple sections and consequently require significant space. Some switchgear assemblies employ an external arcing chamber that limits the configuration of components, equipment, etc., within the switchgear assembly.
Conventional medium voltage switchgear assemblies available in markets, for example, in Europe and Asia are built in accordance with the International Electrotechnical Commission (IEC) standards, and in the North American market need to meet stringent Institute of Electrical and Electronics Engineers (IEEE) requirements, American National Standards Institute (ANSI) and Underwriters Laboratories (UL) requirements. However, these switchgear assemblies have cable connection and bus bar compartments disposed in the rear of each section that are not configured to be accessible from the front and, therefore, make it difficult to install and service electrical components and the bus bars accommodated within these switchgear assemblies, as currently configured. Furthermore, conventional switchgear assemblies built to ANSI standards utilize ring type current transformers that are mounted in such a way that the circuit breaker primary connector arm passes through the transformers when in the connect position. The current transformers are mounted in the circuit breaker compartment behind the shutter between the circuit breaker poles making it difficult to install relay class current transformers in conventional switchgear assemblies that require separate sections for metering and protection. Consequently, there is a need for easy accessibility to the cable connection and bus bar compartments from the front of a new switchgear enclosure (i.e., requires only a single, front-accessible section). Furthermore, there is a need for mounting separate current transformers for each phase with higher burden for relay class applications accessible from the front of the switchgear enclosure for easier accessibility for maintenance and inspection.
Certain conventional switchgear assemblies have attempted to overcome the disadvantage of rear mounted current transformers by incorporating a front-accessible mounting block assembly with limited current transformers configured as a monoblock (i.e., a single, unitary block configuration that accommodates all three phases) including ring or toroidal current transformers, that is adapted to interface with tulip connectors. However, this arrangement presents further disadvantages, in that, removal of the entire monoblock mounting block is required for maintenance and service which is difficult and unwieldy given the actual considerable physical size of these parts. Consequently, there is a need for individually front accessible high accuracy class current transformers for each individual phase.
Conventional ANSI switchgear assemblies do not have or require that the door of the circuit breaker or the voltage transformer be interlocked with the truck mounted unit devices (VCB or VT). This type of arrangement enables the operator to open the door while the voltage transformer is energized and delivering electrical power. Further, this also permits racking in and out operation of the voltage transformer truck and any one of these actions can trigger operational hazards in the event an arc fault is initiated inside the voltage transformer compartment. Consequently, there is a need for an interlocked door for the voltage transformer compartment that insures operator safety. A door interlock that is in communication with the truck would advantageously prevent opening the door when the voltage transformer is in the energized position and the racking in and out operation of the voltage transformer with the door in the open position and provides a shield that prevents discharge in the event of an arc fault.
Therefore, there is a long felt but unresolved need for an arc resistant front accessible metal clad switchgear enclosure that has all necessary medium switchgear components in a single section with a compact footprint and provides front access to all functional compartments, i.e., low voltage control compartment, vacuum circuit breaker compartment, voltage transformer compartment, cable connection compartment and bus bar compartment, and the respective electrical components and equipment accommodated in the medium voltage switchgear enclosure for inspection, testing and maintenance with limited space requirements and without protective gear.